Add a Mime Type for .exe and .dll files. (#21805)

* Add a Mime Type for .exe and .dll files.

Useful for serving downloads of installers.
Could be application/octet-stream, but I hear application/vnd.microsoft.portable-executable is specified by IANA here:

https://www.iana.org/assignments/media-types/application/vnd.microsoft.portable-executable

* Update src/Middleware/StaticFiles/src/FileExtensionContentTypeProvider.cs

Co-authored-by: Chris Ross <[email protected]>

* Update src/Middleware/StaticFiles/src/FileExtensionContentTypeProvider.cs

Co-authored-by: Chris Ross <[email protected]>

Co-authored-by: Chris Ross <[email protected]>

Author: KirillOsenkov

src/Middleware/StaticFiles/src/FileExtensionContentTypeProvider.cs

@@ -104,6 +104,7 @@ public FileExtensionContentTypeProvider()
                 { ".eps", "application/postscript" },
                 { ".etx", "text/x-setext" },
                 { ".evy", "application/envoy" },
+                { ".exe", "application/vnd.microsoft.portable-executable" }, // https://www.iana.org/assignments/media-types/application/vnd.microsoft.portable-executable
                 { ".fdf", "application/vnd.fdf" },
                 { ".fif", "application/fractals" },
                 { ".fla", "application/octet-stream" },